1. Field of the Invention
The present invention generally relates to a pressure-adjustable container, and more particularly to such containers that are typically made of polyester and are capable of being filled with hot liquid. It also relates to an improved sidewall construction for such containers.
2. Statement of the Prior Art
xe2x80x9cHot-fillxe2x80x9d applications impose significant and complex mechanical stress on the structure of a plastic container due to thermal stress, hydraulic pressure upon filling and immediately after capping the container, and vacuum pressure as the fluid cools.
Thermal stress is applied to the walls of the container upon introduction of hot fluid. The hot fluid causes the container walls to first soften and then shrink unevenly, causing distortion of the container. The plastic material (e.g., polyester) must, therefore, be heat-treated to induce molecular changes resulting in a container that exhibits thermal stability.
Pressure and stress also act upon the sidewalls of a heat resistant container during the filling process, and for a significant period of time thereafter. When the container is filled with hot fluid and sealed, there is an initial hydraulic pressure and an increased internal pressure is placed upon the container. As the liquid and the air headspace under the cap subsequently cools, thermal contraction results in partial evacuation of the container. The vacuum created by this cooling tends to mechanically deform the container walls.
Generally speaking, plastic containers incorporating a plurality of longitudinal fiat surfaces accommodate vacuum force more readily. For example, U.S. Pat. No. 4,497,855 (Agrawal et al.) discloses a container with a plurality of recessed collapse panels, separated by land areas, which allows uniformly inward deformation under vacuum force. The vacuum effects are controlled without adversely affecting the appearance of the container. The panels are drawn inwardly to vent the internal vacuum and so prevent excess force being applied to the container structure. Otherwise, such forces would deform the inflexible post or land area structures. The amount of xe2x80x9cflexxe2x80x9d available in each panel is limited, however. As that limit is approached, there is an increased amount of force that is transferred to the sidewalls.
To minimize the effect of force being transferred to the sidewalls, much prior art has focused on providing stiffened regions to the container, including the panels, to prevent the structure yielding to the vacuum force. For example, the provision of either horizontal or vertical annular sections, or xe2x80x9cribsxe2x80x9d, throughout a container has become common practice in container construction. The use of such ribs is not only restricted to hot-fill containers. Such annular sections strengthen the part upon which they are deployed.
Examples of the prior art teaching the use of such ribs are U.S. Pat. No. 4,372,455 (xe2x80x9cCochranxe2x80x9d), U.S. Pat. No. 4,805,788 (xe2x80x9cOta Ixe2x80x9d), U.S. Pat. No. 5,178,290 (xe2x80x9cOta IIxe2x80x9d), and U.S. Pat. No. 5,238,129 (xe2x80x9cOta IIIxe2x80x9d). Cochran discloses annular rib strengthening in a longitudinal direction, placed in the areas between the flat surfaces that are subjected to inwardly deforming hydrostatic forces under vacuum force. Ota I discloses longitudinally extending ribs alongside the panels to add stiffening to the container, and the strengthening effect of providing a larger step in the sides of the land areas. This provides greater dimension and strength to the rib areas between the panels. Ota II discloses indentations to strengthen the panel areas themselves. Ota III discloses further annular rib strengthening, this time horizontally directed in strips above and below, and outside, the hot-fill panel section of the bottle.
In addition to the need for strengthening a container against both thermal and vacuum stress, there is a need to allow for an initial hydraulic pressure and increased internal pressure that is placed upon a container when hot liquid is first introduced and then followed by capping. This causes stress to be placed on the container sidewall. There is a forced outward movement of the heat panels, which can result in a barreling of the container.
Thus, U.S. Pat. No. 4,877,141 (xe2x80x9cHayashi et al.xe2x80x9d) discloses a panel configuration that accommodates an initial, and natural, outward flexing caused by internal hydraulic pressure and temperature, followed by inward flexing caused by the vacuum formation during cooling. Importantly, the panel is kept relatively flat in profile, but with a central portion displaced slightly to add strength to the panel but without preventing its radial movement in and out. With the panel being generally flat, however, the amount of movement is limited in both directions. By necessity, panel ribs are not included for extra resilience, as this would prohibit outward and inward return movement of the panel as a whole.
U.S. Pat. No. 5,908,128 (xe2x80x9cKrishnakumar Ixe2x80x9d) discloses another flexible panel that is intended to be reactive to hydraulic pressure and temperature forces that occur after filling. Relatively standard hot-fill style container geometry is disclosed for a xe2x80x9cpasteurizablexe2x80x9d container. It is claimed that the pasteurization process does not require the container to be heat-set prior to filling, because the liquid is introduced cold and is heated after capping. Concave panels are used to compensate for the pressure differentials. To provide for flexibility in both radial outward movement followed by radial inward movement however, the panels are kept to a shallow inward-bow to accommodate a response to the changing internal pressure and temperatures of the pasteurization process. The increase in temperature after capping, which is sustained for some time, softens the plastic material and therefore allows the inwardly curved panels to flex more easily under the induced force. It is disclosed that too much curvature would prevent this, however. Permanent deformation of the panels when forced into an opposite bow is avoided by the shallow setting of the bow, and also by the softening of the material under heat. The amount of force transmitted to the walls of the container is therefore once again determined by the amount of flex available in the panels, just as it is in a standard hot-fill bottle. The amount of flex is limited, however, due to the need to keep a shallow curvature on the radial profile of the panels. Accordingly, the bottle is strengthened in many standard ways.
U.S. Pat. No. 5,303,834 (xe2x80x9cKrishnakumar IIxe2x80x9d) discloses still further xe2x80x9cflexiblexe2x80x9d panels that can be moved from a convex position to a concave position, in providing for a xe2x80x9csqueezablexe2x80x9d container. Vacuum pressure alone cannot invert the panels, but they can be manually forced into inversion. The panels automatically xe2x80x9cbouncexe2x80x9d back to their original shape upon release of squeeze pressure, as a significant amount of force is required to keep them in an inverted position, and this must be maintained manually. Permanent deformation of the panel, caused by the initial convex presentation, is avoided through the use of multiple longitudinal flex points.
U.S. Pat. No. 5,971,184 (xe2x80x9cKrishnakumar IIIxe2x80x9d) discloses still further xe2x80x9cflexiblexe2x80x9d panels that claim to be movable from a convex first position to a concave second position in providing for a grip-bottle comprising two large, flattened sides. Each panel incorporates an indented xe2x80x9cinvertiblexe2x80x9d central portion. Containers such as this, whereby there are two large and flat opposing sides, differ in vacuum pressure stability from hot-fill containers that are intended to maintain a generally cylindrical shape under vacuum draw. The enlarged panel sidewalls are subject to increased suction and are drawn into concavity more so than if each panel were smaller in size, as occurs in a xe2x80x9cstandardxe2x80x9d configuration comprising six panels on a substantially cylindrical container. Thus, such a container structure increases the amount of force supplied to each of the two panels, thereby increasing the amount of flex force available.
Even so, the convex portion of the panels must still be kept relatively flat, however, or the vacuum force cannot draw the panels into the required concavity. The need to keep a shallow bow to allow flex to occur was previously described in both Krishnakumar I and Krishnakumar II. This, in turn, limits the amount of vacuum force that is vented before strain is placed on the container walls. Further, it is generally considered impossible for a shape that is convex in both the longitudinal and horizontal planes to successfully invert, anyhow, unless it is of very shallow convexity. Still further, the panels cannot then return back to their original convex position again upon release of vacuum pressure when the cap is removed if there is any meaningful amount of convexity in the panels. At best, a panel will be subject to being xe2x80x9cforce-flippedxe2x80x9d and will lock into a new inverted position. The panel is then unable to reverse in direction as there is no longer the influence of heat from the liquid to soften the material and there is insufficient force available from the ambient pressure. Additionally, there is no longer assistance from the memory force that was available in the plastic prior to being flipped into a concave position. Krishnakumar I previously discloses the provision of longitudinal ribs to prevent such permanent deformation occurring when the panel arcs are flexed from a convex position to one of concavity. This same observation regarding permanent deformation is also disclosed in Krishnakumar II. Hayashi et al. also disclose the necessity of keeping panels relatively flat if they were to be flexed against their natural curve.
It is believed that the principal mode of failure in prior art containers is non-recoverable buckling of the structural geometry of the container, due to weakness, when there is a vacuum pressure inside the container. This is especially the case when such a container has been subjected to a lowering of the material weight for commercial advantage.
One means of avoiding such modes of failure is disclosed in International Publication No. WO 00/50309 (xe2x80x9cMelrosexe2x80x9d). Melrose discloses a container having pressure responsive panels that allow for increased flexing of the vacuum panel sidewalls so that the pressure on the containers may be more readily accommodated. Reinforcing ribs of various types and location may still be used, as described above, to still compensate for any excess stress that must inevitably be present from the flexing of the container walls into the new xe2x80x9cpressure-adjustedxe2x80x9d condition by ambient forces.
Containers of the type disclosed in Melrose are known as xe2x80x9cactive cagexe2x80x9d containers. Active cage refers to a type of high-uptake vacuum flex panel that can be smaller in size, that does not need to be encased in a traditional rigid frame, and that can be located nearly anywhere on the outer surfaces of the bottle. Such surfaces are also known as active surfaces. The vacuum flex panels according to Melrose are set inwardly with respect to the longitudinal axis of the container, and are located between relatively inflexible land areas. Preferably, the container includes a connecting portion between the flexible panel and inflexible land areas.
The connector portions are adapted to locate the flexible panel and land areas at a different circumference relative to a center of the container. In a preferred embodiment, the connecting portion is substantially xe2x80x9cUxe2x80x9d-shaped, wherein the side of the connecting portion towards the flexible panel is adapted to flex, substantially straightening the xe2x80x9cUxe2x80x9d-shape when the flexible panel is in a first position and return to the xe2x80x9cUxe2x80x9d-shape when the flexible panel is inverted from the first position. Such connecting portions and land areas form a network of pillars, each of which are set outwardly with respect to the longitudinal axis of the container. The plurality of active surfaces, together with the network of pillars, are spaced about the periphery of the container in order to accommodate vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof.
It has been found that an xe2x80x9cinverted active cagexe2x80x9d would not only provide further freedom in the aesthetic design and ornamental appearance of plastic containers, but would also accommodate such vacuum-induced volumetric shrinkage of those containers. Accordingly, it would be desirable to provide a container with a plurality of active surfaces, each of which is outwardly displaced with respect to the longitudinal axis of the container, and a network of pillars, each of which is inwardly displaced with respect to the longitudinal axis of the container. Such a plurality of active surfaces together with the network of pillars could, thus, be spaced about the periphery of the container for accommodating vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof.
A container having an inverted active cage achieves the above and other objects, advantages, and novel features according to the present invention.
Such a container generally comprises an enclosed base portion, a body portion extending upwardly from the base portion, and a top portion with a finish extending upwardly from the body portion. The body portion includes a central longitudinal axis, a periphery, a plurality of active surfaces, and a network of pillars. Importantly, each of the plurality of active surfaces is outwardly displaced with respect to the longitudinal axis, while each of the network of pillars is inwardly displaced with respect to the longitudinal axis. The plurality of active surfaces, together with the network of pillars, are spaced about the periphery for accommodating vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof.
The body portion may suitably comprise a hollow body formed generally in the shape of a cylinder. As a result, a cross-section of that body in a plane perpendicular to the longitudinal axis may comprise a circle, an ellipse, or an oval.
Alternatively, the body portion may suitably comprise a hollow body formed generally in the shape of a polyhedron (i.e., a solid bounded by planar polygons). In those instances where the body portion is formed generally in the shape of a polyhedron, such shape may more specifically be a parallelepiped (i.e., a polyhedron all of whose faces are parallelograms).
According to one aspect of the present invention, there is provided two or more controlled deflection flex panels, each of which has an initiator region of a predetermined extent of projection and a flexure region of a greater extent of projection extending away from the initiator region. As a result, flex panel deflection occurs in a controlled manner in response to changing container pressure. Each of the plurality of active surfaces, thus, comprises a controlled deflection flex panel or vacuum flex panel.
According to another aspect of the present invention, the body portion comprises two or more vacuum flex panels. In various embodiments as shown as described herein, the body portion comprises three, five, six, and twelve such vacuum flex panels.
The network of pillars of the present invention preferably comprises one or more grooves separating each of the plurality of active surfaces. Each groove extends substantially between the top portion and the base portion. In one embodiment, a top portion of each groove is displaced from a bottom portion thereof by approximately sixty degrees around the periphery of the container. A portion of each of the plurality of active surfaces, thus, extends by approximately one-third around the periphery of the container. According to yet another aspect of the present invention, the plurality of active surfaces and network of pillars together comprise an active cage. Such an active cage may comprise a substantially rigid cage or a substantially flexible cage.
In one embodiment, the network of pillars comprises a substantially sinusoidal-shaped groove extending about the periphery of the container. That groove extends substantially between the top portion and the base portion.
Each of the plurality of active surfaces, as noted above, further comprises an initiator portion and a flexure portion. The initiator portion and the flexure portion are preferably positioned substantially parallel to and in the direction of the longitudinal axis within each of the plurality of active surfaces.
The network of pillars may also comprise an annulus. In one embodiment, the annulus comprises a substantially sinusoidal-shaped groove extending about the periphery of the container. In this embodiment, at least one of the initiator portions is positioned above the substantially sinusoidal-shaped groove and at least another of the initiator portions is positioned below the substantially sinusoidal-shaped groove.
Alternatively, the network of pillars may comprise a plurality of grooves positioned substantially parallel to and in the direction of the longitudinal axis within each of the plurality of active surfaces. The network of pillars in this embodiment may also comprise an annulus. Such an annulus may comprise a substantially sinusoidal-shaped groove extending about the periphery of the container. In this embodiment as well, each of the plurality of active surfaces may further comprise an initiator portion and a flexure portion. The initiator portion and the flexure portion are positioned substantially parallel to and in the direction of the longitudinal axis within each of the plurality of active surfaces.
At least one of the initiator portions is positioned above the substantially sinusoidal-shaped groove and at least another of the initiator portions is positioned below the substantially sinusoidal-shaped groove.
In a container having an enclosed base portion, a body portion extending upwardly from the base portion and including an active cage that is adapted to accommodate vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof, and a top portion with a finish extending upwardly from the body portion, the present invention also provides an improvement comprising inverting the active cage.
In a container having an enclosed base portion, a body portion extending upwardly from the base portion, and a top portion with a finish extending upwardly from the body portion, wherein the body portion includes a periphery and an active cage disposed about the periphery to accommodate vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof, the present invention further provides the improvement comprising inverting the active cage.
An active cage for a plastic container having a central longitudinal axis and a periphery, in accordance with the oresent invention, comprises a plurality of active surfaces; and a network of pillars; wherein, with respect to the longitudinal axis, each of the plurality of active surfaces is outwardly displaced and each of the network of pillars is inwardly displaced, and the plurality of active surfaces together with the network of pillars are spaced about the periphery for accommodating vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof.
Also disclosed is an inverted active cage for a plastic container, which comprises a plurality of active surfaces, each of which is outwardly displaced with respect to a longitudinal axis of the container; and a network of pillars, each of which is inwardly displaced with respect to the longitudinal axis. The inverted active cage according to the present invention spaces the plurality of active surfaces together with the network of pillars about the periphery of the container in order to accommodate vacuum-induced volumetric shrinkage of the container resulting from a hot-filling, capping and cooling thereof. The inverted active cage may also comprise an annulus, and the annulus may comprise a waist.
The foregoing and other features and advantages of the invention will become more apparent from the following detailed description of exemplary embodiments thereof, when consider in conjunction with the accompanying drawings wherein: